Tobacco use and prevalence of chronic obstructive pulmonary disease (COPD) are significantly higher among veterans than non-veteran population. Airway and pulmonary vascular remodeling is the most critical process in the pathogenesis of COPD. Large amounts of reactive oxygen species (ROS) are released from activated inflammatory cells and other lung cells in COPD or from tobacco smoke (TS) per se. ROS are implicated in the development of airway and pulmonary vascular remodeling. However, little has been known about how ROS and TS lead to these pathological alterations. We have found that ROS and TS activates calpain in bronchial and pulmonary artery smooth muscle cells (BSMCs and PASMCs) and that calpain mediates cell proliferation and collagen-I synthesis in PASMCs. Calpain is a family of calcium-dependent non- lysosomal neutral cysteine endopeptidases that act via limited proteolysis of substrate proteins in mammalian cells, including BSMCs and PASMCs. We have recently reported for the first time that global inhibition of calpain prevents pulmonary vascular remodeling induced by chronic hypoxia and monocrotaline. In preliminary experiments, we found that the specific calpain inhibitor, MDL28170, prevented ROS-induced increases in cell proliferation and protein levels of collagen-I in BSMCs and PASMCs. Transforming growth factor (TGF)/Smad pathway have been shown to play important roles in airway and pulmonary vascular remodeling. We have reported that calpain activates TGF1 by cleaving latent TGF1. This proposal is to study a novel hypothesis that calpain mediates ROS- and TS-induced cell proliferation and collagen synthesis in airway and pulmonary vascular smooth muscle cells via activation of intracellular TGF1 in TS-induced COPD. The protein and activity of calpain, cell proliferation and collagen synthesis will be determined in BSMCs and PASMCs with or without treatment of H2O2 and TS. Calpain activity will be manipulated using specific inhibitor, siRNA and over-expression of calpastatin genes. A novel intracrine TGF1 pathway will be studied in H2O2- and TS-treated cells. Moreover, the role of calpain in airway and pulmonary vascular remodeling will be evaluated in a COPD animal model using innovative inducible global and smooth muscle-specific calpain knockout mouse line. Finally, calpain will be pharmacologically targeted using a specific calpain inhibitor MDL28170 in a TS-induced COPD rat model. This proposal is novel because it will identify calpain as a mediator in airway and pulmonary vascular remodeling and calpain serves this role by activating intracellular TGF1 in BSMCs and PASMCs. A better understanding of the mechanistic insight will provide a strong rationale for manipulating calpain activities in the treatment of lung diseases such as COPD, pulmonary hypertension and cor pulmonale. Completion of this project will help find novel treatments for COPD and in turn improve the life and care of veterans.